The invention relates to a masking system for the masking of a crank chamber of an internal combustion machine during a surface treatment of a cylinder running surface as well as to the use of a masking system in accordance with the present invention.
The thermal coating of cylinder running surfaces of internal combustion engines by different thermal spray processes is state of the art today and is in particular widely used on engines for motor vehicles of all types, but not just here. Usually, the corresponding cylinder running surfaces are activated before the thermal coating by different processes, e.g. by corundum blasting, hard cast blasting, high-pressure water blasting, various laser processes or other activation processes known per se. Substrates of light metal alloys on an Al or Mg base are most frequently pre-treated and subsequently coated.
A widely used type of engine is an engine in a V design, that is, an engine which has two cylinder rows running parallel to one another, with the two longitudinal axes of two adjacent cylinder liners which each belong to one of the two cylinder rows being inclined by a specific angle with respect to one another, whereby the characteristic V shape of the engine block of an engine in V design arises.
In such V engines, the risk exists on thermal coating that, during a surface treatment of the cylinder running surfaces, e.g. on the activation, cleaning or another pre-treatment of the cylinder running surfaces, surfaces of the crank chamber of the engine block or cylinder running surfaces of adjacent cylinder bores can also be affected in an uncontrolled manner. Corresponding problems also occur above all on the thermal coating of the cylinder wall of a cylinder of the internal combustion engine. On the coating of a cylinder running surface of a cylinder bore of a first cylinder row, vapors, e.g. metal vapors of the coating material, which can never be completely avoided in thermal coating, can namely be deposited on the cylinder wall of an adjacent cylinder.
Due to the deposition of the metal vapors at the relatively cold walls on the cylinder wall of the cylinder, e.g. of the second cylinder row, this cylinder wall in the second cylinder row is contaminated by the metal vapors, which inter alia has a negative effect on the adhesion of a coating likewise still to be applied to this cylinder later. In addition, a contamination by unmelted particles and by overspray is to be feared and also the inner surfaces of the crankcase can be contaminated in a disadvantageous manner or also be affected.
A further problem is the heating of the engine block by the thermal coating process. Since the difference in the thermal coefficient of expansion between the thermal spray coating and the substrate can be relatively high, a temperature of the substrate of more than 120° C., with this substantially having to be understood as a type of mean temperature of the engine block, has a negative effect on the internal stress level of the layers, and above 150° C. there is even the risk that the component made from a light metal alloy, that is, the engine block, suffers deformation of the material and thus becomes unusable.
This problem becomes particularly clear when one looks at the thermal coefficients of expansion of typical materials used: typical coefficients of expansion of thermal spray coatings from alloys on an iron base lie e.g. at approx. 11×10−6/° C., whereas typical thermal coefficients of expansion of substrates on an aluminum base can lie at approx. 23×10−6/° C. and for substrates on a magnesium base typically at 27×10−6/° C. This means that typical thermal coefficients of expansion of the substrates, that is, of the material from which the engine blocks are made, are of an order of magnitude of more than twice as large as the thermal coefficients of expansion of the thermal spray coatings sprayed on.
Various apparatuses are known in the prior art which in particular attempt to solve the problem of the contamination of cylinder running surfaces with the previously mentioned metal vapors.
Apparatuses are thus known in which cylinder bores which are not coated are sealed with a type of inflatable balloon, which can, however, lead to heat accumulation and aggravate the above-mentioned problems with the thermal coefficients of expansion even more. Other systems are in use in which covers are introduced through the crankshaft housing for the protection of the cylinder bores which are not to be coated. The thermal problems are also ultimately not completely solved here and, which is at least just as important, the use of all known systems can only be automated with great difficulty, if at all, in particular in the case of engines in the V design, so that the coating process ultimately becomes very expensive because a lot of manual work is required in the coating of a large number of engine blocks.